Triangular numbers having only 1 or 2 different digits in base 10.

Terms

a(0) =0a(1) =1a(2) =3a(3) =6a(4) =10a(5) =15a(6) =21a(7) =28a(8) =36a(9) =45a(10) =55a(11) =66a(12) =78a(13) =91a(14) =171a(15) =300a(16) =595a(17) =666a(18) =990a(19) =1711a(20) =2211a(21) =3003a(22) =5050a(23) =5151a(24) =5565a(25) =5995a(26) =6555a(27) =8778a(28) =10011a(29) =66066